1. Field of the Invention
The present invention relates to the field of cooling systems, and in particular to a method and apparatus for serial coolant flow control.
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2. Background Art
Many systems require cooling to function properly. Some systems accomplish cooling through the flow of a coolant through the system. In many cooling systems, it is desirable to increase the amount of coolant flowing through the system. However, current schemes to increase coolant flow involve unacceptably increasing the size of coolant flow control units. This problem can be better understood by a review of cooling systems.
Many systems (e.g. general purpose computers, automobiles and nuclear reactors) use a coolant to cool the system. Coolants can be any of a variety of substances, including light water, heavy water, air, carbon dioxide, helium, liquid sodium, liquid sodium-potassium alloy, and hydrocarbons (oils). Such substances are good conductors of heat and serve to carry the thermal energy produced by the system away from the system. A system draws fresh coolant in through one or more coolant intakes. The coolant, then, passes over system components which require cooling. Heat transfers from the system components to the coolant, thus cooling the components. Then, the heated coolant is expelled through one or more coolant exhausts.
The flow of coolant is often driven by a pressure difference between the interior and exterior of the system. The pressure difference is created by a coolant flow control unit. In a negatively pressurized system, a coolant flow control unit forces coolant out through a coolant exhaust. The smaller amount of coolant in the system causes the pressure inside the system to drop. Thus, the pressure inside the system will drop below the pressure outside the system near one or more coolant intakes. The pressure difference forces fresh coolant into the system through one or more coolant intakes. The coolant intakes and exhausts are positioned so that coolant flows through the parts of the system which require cooling. Heat transfers from the system parts to the coolant, and the coolant carries the heat out of the system.
Similarly, in a positively pressurized system, a coolant flow control unit forces coolant in through a coolant intake. The larger amount of coolant in the system causes the pressure inside the system to increase. Thus, the pressure inside the system will rise above the pressure outside the system near one or more coolant exhausts. The pressure difference forces heated coolant out of the system through one or more coolant exhausts. The coolant intakes and exhausts are positioned so that coolant flows through the parts of the system which require cooling. Heat transfers from the system parts to the coolant, and the coolant carries the heat out of the system.
FIG. 1 illustrates a system which cools through a negatively pressurized cooling system. The coolant flow control unit (100) causes the pressure on the inside of the system (110) near the coolant exhaust (120) to be higher than the pressure on the outside of the system (130). As a result, heated coolant (140) is expelled from the system through the coolant exhaust. The decrease in the amount of coolant in the system causes the pressure inside the system near the coolant intake (150) to be lower than the pressure outside the system. Thus, fresh coolant (160) flows into the system through the coolant intake. The fresh coolant will flow from the coolant intake, over the vital system components (170) and to the coolant exhaust.
Coolant flow controllers drive the flow of coolant through a system. Controllers commonly utilize angled rotating blades. For example, a common household fan is a set of angled rotating blades which forces coolant (air) to flow in the system. As the blades pass through the coolant, coolant is pushed towards the trailing edge of the blade. Thus, the angled rotating blades created a flow of coolant. The rate the coolant flows tangential to the direction of the blade is termed xe2x80x9cforward velocity.xe2x80x9d The rate the coolant flows in the direction opposite the direction of the blade rotation is termed xe2x80x9cswirl velocity.xe2x80x9d
FIG. 2 illustrates coolant flow caused by angled rotating blades. Blades 1 (200), 2 (205) and 3 (210) rotate in the direction indicated by arrow 1 (215). Arrows 2 (220), 3 (225) and 4 (230) represent the flow of coolant caused by the angled rotating blades. The flow of coolant is the combination of a forward velocity (235) and a swirl velocity (240).
One common desire in coolant flow controller design is to increase the pressure and flow generated by the controller. The addition of another set of identical rotating blades is a method which fails to generate greater pressure or flow., Since the coolant is already flowing at the same angle of the second rotating blade, the second rotating blade is unable to transfer additional energy to the flowing coolant. Thus, a sequence of sets of identical angled rotating blades fails to increase pressure or flow.
FIG. 3 illustrates coolant flow caused by a sequence of two identical sets of angled rotating blades. Blades 1 (300), 2 (305) and 3 (310) rotate in the direction indicated by arrow 1 (315). Blades 4 (320), 5 (325) and 6 (330) rotate in the direction indicated by arrow 2 (335). Arrows 3 (340), 4 (345) and 5 (350) represent the magnitude and direction of the flow of coolant caused by blades 1, 2 and 3. Arrows 6 (355), 7 (360) and 8 (365) represent the magnitude and direction of the flow of coolant caused by blades 4, 5 and 6. Because the sets of rotating blades are identical, the magnitude and direction of flow caused by blades 1, 2 and 3 are equal to the magnitude and direction of flow caused by blades 4, 5 and 6. Thus, the second set of blades does not increase the pressure or flow.
One prior art method for increasing pressure and flow involves increasing-the size of the rotating blades. However, for applications where size is limited, this method is not appropriate. Another prior art method for increasing pressure and flow involves increasing the speed at which the blades rotate. However, physical constraints limit the speed at which a set of blades rotate. Once this maximum speed is reached, this method fails to produce further increases in pressure and flow.
The present invention provides a method and apparatus for serial coolant flow control. In one embodiment of the present invention, two or more sets of angled rotating blades are used in series to increase the coolant pressure and flow. In this embodiment, the rotational direction of a set of blades is the reverse of the rotational direction of any set of blades next to it.
In one embodiment, the angles of the blades are such that. the forward velocity created by a set of blades is in the same direction as forward velocities created by other sets of blades in the system. In one embodiment, the blades of one set form a right angle with the blades of any set next to it.
In one embodiment, the coolant flow controller is a fan. In another embodiment, the coolant is air. In yet another embodiment, the system being cooled is an electronic system (e.g., a computer).